<b-menu style="max-width: 200px;">
  <b-menu-item value="opt-1">Option 1</b-menu-item>
  <b-menu-item value="opt-2">Option 2</b-menu-item>
  <b-menu-item value="opt-3">Option 3</b-menu-item>
  <b-divider></b-divider>
  <b-menu-item value="disabled" disabled>Disabled</b-menu-item>
</b-menu>

<script>
  const menu = document.querySelector('b-menu');
  menu.addEventListener('select', (event) => {
    console.log(event.detail.item.value);
  });
</script>